This paper presents a quantum mechanical analysis of fluctuation theorems (FTs) and counting statistics in nonequilibrium systems. The authors derive FTs for both closed and open quantum systems driven out of equilibrium by external forces, as well as for systems in nonequilibrium steady states. The derivation is based on a two-point measurement approach, which allows for the calculation of probabilities for forward and time-reversed processes. The paper discusses applications to fermion and boson transport in quantum junctions, and presents quantum master equations and Green's functions techniques for computing energy and particle statistics. The paper begins with an introduction to the fluctuation-dissipation theorem and its extension to nonequilibrium systems. It then presents the general derivation of FTs, including transient and steady-state theorems. The transient FTs include the work fluctuation theorem for isolated and closed driven systems, as well as a FT for direct heat and matter exchange between two systems. The steady-state FTs are derived for heat and matter exchange between two reservoirs through an embedded system. The paper also discusses the application of FTs to heat and matter transfer statistics in weakly-coupled open systems. It presents a generalized quantum master equation and its applications to particle counting statistics in various models of interest in nanoscience. The paper further explores a many-body approach to particle counting statistics, using a Liouville space formulation and electron counting statistics for direct-tunneling between two systems. The authors also discuss nonlinear coefficients and their implications for nonequilibrium constraints. The paper concludes with a discussion of the implications of FTs for quantum systems, including their connection to time-reversal symmetry, large deviation theory, and the derivation of generalized quantum master equations. The paper provides a comprehensive overview of the theoretical foundations and applications of FTs in quantum systems, highlighting their importance in understanding nonequilibrium fluctuations and counting statistics in quantum systems.This paper presents a quantum mechanical analysis of fluctuation theorems (FTs) and counting statistics in nonequilibrium systems. The authors derive FTs for both closed and open quantum systems driven out of equilibrium by external forces, as well as for systems in nonequilibrium steady states. The derivation is based on a two-point measurement approach, which allows for the calculation of probabilities for forward and time-reversed processes. The paper discusses applications to fermion and boson transport in quantum junctions, and presents quantum master equations and Green's functions techniques for computing energy and particle statistics. The paper begins with an introduction to the fluctuation-dissipation theorem and its extension to nonequilibrium systems. It then presents the general derivation of FTs, including transient and steady-state theorems. The transient FTs include the work fluctuation theorem for isolated and closed driven systems, as well as a FT for direct heat and matter exchange between two systems. The steady-state FTs are derived for heat and matter exchange between two reservoirs through an embedded system. The paper also discusses the application of FTs to heat and matter transfer statistics in weakly-coupled open systems. It presents a generalized quantum master equation and its applications to particle counting statistics in various models of interest in nanoscience. The paper further explores a many-body approach to particle counting statistics, using a Liouville space formulation and electron counting statistics for direct-tunneling between two systems. The authors also discuss nonlinear coefficients and their implications for nonequilibrium constraints. The paper concludes with a discussion of the implications of FTs for quantum systems, including their connection to time-reversal symmetry, large deviation theory, and the derivation of generalized quantum master equations. The paper provides a comprehensive overview of the theoretical foundations and applications of FTs in quantum systems, highlighting their importance in understanding nonequilibrium fluctuations and counting statistics in quantum systems.